Patent GB-1395754-A (GB)
Title: Weldability of articles made from plastics foam
IPC: B29C65/38
Filed: 1972-03-30
Abstract: 1395754 Laminated plastics foam G POHL 30 March 1972 [2 April 1971 13 May 1971] 15185/72 Heading B5N [Also in Divisions B2 and D1] The weldability of articles made from plastics foams to make laminates is improved by bring- ing a plastics foam article having at least some open cells into contact with particulate thermoplastics solid which when introduced into the foam renders the foam more easily weldable, and at or after contact between the foam article and the particulate solid distorting the article whereby the solid enters at least some of the open cells of the plastics foam as a result of the foam being distorted and subsequently removing the distorting force. The article may be distorted by being pulled, pressed, stamped, bent, sheared, twisted or vibrated. The article may be in sheet form and distorted by applying a tensile load in at least one of its principal planes and optionally also applying at least one compressive load. The welding aid may be applied by means of an engraved screen roller. The article containing the welding aid may be heated until the thermoplastic welding aid particles soften and become permanently connected to the adjacent walls of the cells in the foam material. Preferably the welding aid is applied to both surfaces of foam webs and the webs distorted at least once from each side. The foam may be of polyethylene, polystyrene, polyurethane. The welding aids are thermoplastic materials, preferably synthetic thermoplastic materials, e.g. homopolymers and copolymers of vinyl chloride, vinyl acetate, vinyl propionate, vinylidene chloride, acrylates, methyl methacrylates, polyamides. The treated foams may be welded by high-frequency welding, thermal contact welding or thermal impulse welding. High frequency welding can be used to shape or stamp the foam articles, or to make laminates by connecting their surface to one or more similar or different articles on one or more sides. Covering material may be welded to one or both surfaces of a foam web. Suitable covering materials are textiles made from natural or synthetic fibres in the form of woven or knitted fabrics or fleeces or sheets of natural synthetic polymers. As shown in the figure a foam web 2 is contacted with finely divided welding aid by applicator apparatus comprising a funnel-shaped reservoir 3 for the welding aid 4, a doctor blade 5 which scrapes the welding aid leaving the open mouth of the reservoir 3 on to the engraved surface 6 of applicator roller 7 which transfers the welding aid to the surface of the foam as a line screen or grid. Backer roll 9 presses the foam web on to the engraved roller 7 and a brush 11 is provided to brush surplus welding aid off the applicator roll surface 6. The foam web 2 is then distorted by two pairs of rollers 13, 14 and 15, 16. The web is drawn off by the roller 16 provided with a drive 19 followed by transmission 20 with a variable transmission ratio set by means of lever 21. Rollers 13, 14 are not driven, and roller 14 is provided with a brake 22 to produce the distortion, the braking force exerted on the web 2 being set by adjusting means 23 and detent 24. An optional bearing station 25 may be situated between the pairs of rollers and may comprise two beater drums 28, 29 with beater strips 26, 27. The drum 29 may have its foam drive 30 to relieve tensile stressing of the foam web. A mobile carriage 31 with a brake shoe 32 operable by means of cam 33 can be locked in position anywhere along its guide rails 34 or released for adjustment purposes. The beater strips 26, 27 mesh like gears and the flanks of the strips are highly rounded so that only the intermittent distortion of the web 2 at 35 takes place. After passage through the rollers 15, 16 relaxation of the web takes place and it returns almost completely to its original thickness. The web is then advanced by endless belt conveyer 36 through thermo-fixing zone 37 provided with supply nozzles 38 for hot air. The fixing zone may be followed by a cooling zone (not shown). The other side of the web may be coated in a similar manner in area 41. The foam web 2 is then carried by belt conveyer 42 to heating unit 43 which heats it with hot air until the covering webs 44 and 45 can be calendered on in the gap between a pair of rollers giving a finished 3-ply laminate web 46. Alternatively the thermal bonding of convering materials to the web 2 may be effected by flame bonding or by means of adhesive. In the drawing the adhesive is applied to the underside 47 of the covering material web 44 by applicator 49 with a plurality of rollers and a backed-up roller, and to the top of the foam web 2 and the top 48 of the covering web 45 by nozzle 50, 51. Suitable applications of products are foamed padding, e.g. for seating in motor cars, railway trains, ships and aircraft and for other furniture, mattresses, bed coverings, padding for clothing, tents, camping gear, cooling bags and other cooling receptacles, perambulators, shoes, bags, luggage.